Analysis and Investigation of Thermal Runaway Propagation for a Mechanically Constrained Lithium-Ion Pouch Cell Module

Abstract

In this paper, tests and analysis of thermal runaway propagation for commercial modules consisting of four 41 Ah Li-ion pouch cells are presented. Module samples were tested at 100% state-of-charge and mechanically constrained between two steel plates to provide thermal and mechanical contact between the parts. Voltage and temperature of each cell were monitored during the whole experiment. The triggering of the exothermal reactions was obtained by overheating one cell of the stack with a flat steel heater. In preliminary studies, the melting temperature of the separator was measured (from an extracted sample) with differential scanning calorimetry and thermogravimetric analysis techniques, revealing a tri-layers separator with two melting points (≈135 °C and ≈170 °C). The tests on module level revealed 8 distinct phases observed and analyzed in the respective temperature ranges, including smoking, venting, sparkling, and massive, short circuit condition. The triggering temperature of the cells resulted to be close to the melting temperature of the separator obtained in preliminary tests, confirming that the violent exothermal reactions of thermal runaway are caused by the internal separator failure. Postmortem inspections of the modules revealed the internal electrical failure path in one cell and the propagation of the internal short circuit in its active material volume, suggesting that the expansion of the electrolyte plays a role in the short circuit propagation at the single cell level. The complete thermal runaway propagation process was repeated on 5 modules and ended on average 60 s after the first thermal runaway triggered cell reached a top temperature of 1100 °C.

Battery Performance, Ageing, Reliability and Safety

“…Finally, given the risk of ignition or explosion in the event of a defect or misuse, improving the operational safety of these components is essential [26][27][28]. To investigate this, abuse tests can be performed and/or accidents can be analysed.…”

Thermal Runaway Early Warning and Risk Estimation Based on Gas Production Characteristics of Different Types of Lithium-Ion Batteries

“…Several factors contribute to the safety concerns surrounding LIBs. These include mechanical abuse (e.g., crushing or nail penetration), thermal abuse, and electrical abuse (such as overcharging, over-discharging, and internal short circuits) [1][2][3][4][5]. A primary mechanism underlying these safety issues is the accelerated heat generation in the battery relative to its heat dissipation.…”

The Polarization and Heat Generation Characteristics of Lithium-Ion Battery with Electric–Thermal Coupled Modeling

“…Currently, electric vehicles powered by lithium-ion batteries face several challenges, including limited driving range [1], slow charging times [2,3], battery temperature inconsistencies [4][5][6], the risk of thermal runaway [7,8], and short battery life [9,10]. Researchers have concentrated on increasing the energy density of lithium-ion batteries to tackle the issue of restricted range.…”